Cellulosic structure and method of preparing same



Patented May 3, 1938 UNITED STATES PATENT OFFICE CELLULOSIC STRUCTURE AND METHOD OF PREPARING SAME poration of Delaware No Drawing. Application March 19, 1935, Serial No. 11,817

10 Claims.

This invention relates to improvements in cellulosic structures, and more particularly it relates to improvements in cellulosic pellicles whereby to materially reduce the cost of production and increase their value to the consumer, and methods for producing the same.

Transparent, non-fibrous pellicles of cellulosic materials have been produced heretofore by extruding a cellulosic dispersion for example,

into a coagulating and/or regenerating bath, from which the coagulated or regenerated film is passed through suitable purification solutions, for example, desulfuring, bleaching, and washing solutions, then through a softener solution from which it is led over a series of dryer rolls to be finally collected in the form of a. roll.

One very objectionable disadvantage in the production of transparent, non-fibrous, cellulosic films by the viscose or similar process, resides in the very material shrinkage of such films during their passage over the dryer rolls. It is customary to maintain the surfaces of the various dryer rolls as smooth as possible to prevent marring of the pellicle during its passage thereover. Since nonfibrous, transparent, cellulosic films are also very smooth, they are substantially free to shrink in width due to loss of moisture, even though they may be stretched comparatively tautly between rolls. This shrinkage commonly amounts to from to and may, under adverse conditions, be as high as or more based on the width of the final dry film.

It has now been found that this objectionable shrinkage of cellulosic sheets or films during dryingthereof can be very materially reduced, if not substantially eliminated, without noticeable loss in quality of the resulting pellicle It is therefore an object of this invention to provide a method for drying films, sheets or pellicles of non-fibrous, cellulosic materials with a reduced shrinkage thereof.

It is another object of this invention to provide a method of drying films, sheets or pellicles of non-fibrous, cellulosic materials with a reduced shrinkage and without noticeable loss in quality of the resulting product.

It is a further object of this invention to produce a non-fibrous, cellulosic film, sheet or W pellicle, having a greater covering area per weight of material. v

It is a still further object of this invention to produce a non-fibrous, cellulosic film, sheet or pellicle having a greater covering area per length of extrusion orifice opening.

viscose, through an elongated extrusion orifice.

Other objects of the invention will appear hereinafter.

The objects of this invention may be accomplished in general by applying a material in or on the pellicle or film, after the formation thereof, 5 which will produce a certain amount of tackiness or slight adhesion between the pellicle and the. dryer rolls during their contact with each other.

The process of this invention is applicable to cellulosic pellicles which are smooth, dense, nonfibrous and substantially non-porous, and particularly those water-sensitive cellulosic pellicles which may be obtained by coagulation and/or regeneration from aqueous cellulosic dispersions, including regenerated cellulose; cellulose ethers 15 such as glycol cellulose, lowly substituted methyl or ethyl cellulose, cellulose glycolic acid or cellulose phthalic acid; lowly esterified cellulose esters or ether esters, and the like.

In order to set forth more clearly the details of the invention without prolixity, it will be described with specific reference to pellicles of regenerated cellulose; it is to be understood however that the invention may be likewise applied to the production of other cellulosic pellicles of the type mentioned above in any obvious manner.

In accordance with the process of this invention, the substance to be applied on the pellicles to prevent shrinking thereof is preferably applied to pellicles in their gel state, that is, as they are obtained in the course of manufacture in the purified and washed but undried state. It is possible, however, to apply the same to pellicles which have been dried or dried and later subjected to a re-wetting step prior to the treatment process of this invention. Obviously, it is much more economical and practical to work with the pellicle in the gel state. Although transparent pellicles are to be preferred, it is within the scope of the invention to use pigmented, colored, or otherwise decorated pellicles. The process furthermore does not interfere with subsequent treatments, including lamination, coating, gluing, or the like. Thus, the products of this invention may be provided with coatings, such as, for example, moistureproof surface coatings, without harmful effect due to the treatment according to this invention.

These shrinkage-preventing agents are preferably applied to gel regenerated cellulose sheets during impregnation of the sheets with the usual softening agent, such as, glycerol, ethylene glycol, diethylene glycol, triethylene glycol, invert cane sugar, glucose, sorbitol, calcium chloride, triethanolamine, carbamide, or a suitable combination thereof, or immediately after such impregnation with the softening agent. The shrinkagepreventing agents may be applied to the pellicles as aqueous dispersions or solutions in the treating bath containing the aqueous softener solution, and just prior to drying thereof. Before the pellicle enters the dryer, the excess liquid may be removed by suitable means, such as squeeze rolls, scraper rods, doctor knives, or the like. The amount of shrinkage-preventing agent applied may be controlled by adjusting the concentration of the agent in the treating bath or by varying the amount of excess removed. If it is desired to apply the shringage-preventing agent separately, the pellicle may be treated with the softener bath, the excess removed, and then the liquid or molten shrinkage-preventing agent or the solution or dispersion or emulsion of shrinkage-preventing agent applied by dip rolls, sprays, or the like. When a water-soluble softener is used, it is preferred not to immerse the softerner-treated pellicle in a separate aqueous treating bath containing only a solution of slu'inkage-preventing agent since a part of the softener would thereby be removed from the pellicle.

It has been found that a large variety of materials may be used as shrinkage-preventing agents in the practice of this invention. Generally speaking, those substances which remain slightly tacky or sticky'or which exhibit rather high frictional coefficients will be found useful. More particularly substances having rather large molecules which do not penetrate the pellicular structure but are deposited more as a surface layer on the pellicle will be of value. The substances having these characteristics will generally fall into one of two classes, namely, those which are water-soluble and those which though water-insoluble can be readily dispersed, colloidized or emulsified in water. The last mentioned class, namely, the water-insoluble class comprising resinous materials is generally preferable. Among the substances of outstanding utility, irrespective of the above-mentioned classification, may be mentioned dewaxed shellac, cumar (cumarone) resins, rosin, salts of rosin or the rosin acids such as sodium rosinate or sodium abietate. Other readily dispersible resinous substances include the so-called water-soluble alkyd resins (i. e. those which are derived by the interaction of polyhydric alcohols and polybasic acids, with or without modifying ingredients, and which are dispersible in an aqueous ammonia solution), other alkyd resins which are dispersible by means of suitable emulsifying agents, phenol-aldehyde resins, halogenated diphenyl resins, polymerized terpene resins or even drying oils which have been treated so that they have reached the stage of nearly complete dryness, such as blown tung oil. Among the other useful substances, the bori-borate resins obtained by the condensation of boric acid with polyhydric alcohols such as glycerol, glycol, diethylene glycol, etc., and commonly sold under the trade-name Aquaresin",

dispersion of shrinkage-preventing agents, any

of the well-known materials capable of functioning in this manner may be used, the choice being dependent on the substance to be emulsified.

Thus an aqueous ammonia solution may sufllce, or a small amount of a soap such as sodium oleate, triethanolamine stearate, or emulsifiers such as the sulfonated oils and their salts, e. g. sodium petroleum sulfonate, or the alkali metal salts of sulfuric acid half-esters of the higher fatty alcohols such as stearyl, oleyl, lauryl, cetyl or myristyl alcohols, e. g. sodium oleyl sulfate, may be used.

Optionally, stabilizing agents may be added to the emulsion. Alternatively, in some cases. small amounts of organic solvents may be used to facilitate the preparation of suitable aqueous dispersions. Furthermore any suitable procedure may be employed for introducing the various substances into the dispersions or treating baths and/or for maintaining the treating baths at proper concentration by compensating for the loss of material from the treating bath as it is removed by the pellicle in the course of its passage therethrough. The treating bath may contain solutions, dispersions, suspensions, emulsionsand/ or colloidal solutions depending on the choice of shrinkage-preventing substance and/or the product desired.

Preferably only very minute quantities of shrinkage-preventing agent are applied to the transparent, regenerated cellulose pellicles, which substances, after drying of the pellicle, will usually and preferably amount to less than 2% of the product and may even amount to as little as a few hundredths of one per cent.

For the practice of the invention, it is usually most convenient to prepare concentrated solutions, dispersions, or the like, of suitable shrinkage-preventing compositions and then appropriate amounts of these concentrates may be added to the proper treating bath in order to produce the results desired.

Because of the usual tacky nature of the shrinkage-preventing materials, the treated pellicle, after drying, is preferably provided with a surface coating to avoid objectional adhesion of contiguous pellicular surfaces although in many instances the treated but uncoated pellicle may be useful or, indeed, preferable for certain purposes. When a surface coating is applied it may be of any type desired so long as it provides a smooth, non-tacky surface. Preferably it will be transparent and if desired it may be moistureproof. Various varnishes, lacquers or the like will be found useful depending on the ultimate characteristics desired of the product.

The following examples, which are merely to be taken as illustrative in nature, disclose sizing compositions and methods for applying the same to cellulosic pellicles which may be used to enable production of relatively wide pellicles within the spirit of the invention.

Mixture of the above mentioned ingredients results in a substantially clear, colloidal dispersion of the dewaxed shellac. This concentrated solution may be added to the treating bath in an amount sufllcient to provide a dewaxed shellac concentration of about 0.05-1.0%. If the sizing is added to the softener bath so as to effect simultaneous softening and sizing, the softener content may be adjusted to about '47%, depending on the gage of the pellicle and the amount of softener desired. After the pellicle has been passed through the treating bath, the excess bath is removed, as by squeeze rolls, and the pellicle is led over a series of heated dryer rolls. The dewaxed shellac clinging to the pellicle surface provides a tackiness between the pellicle and the dryer rolls which prevents transverse slipping of the pellicle to such an extent that when the final dried pellicle is secured, the width is or even more, greater than the width of a pellicle prepared in the usual way without the use of the sizing composition. The dried film is tack-free and is suit-' able. for all uses to which the ordinary commercial" product may be put including subsequent coating, as for example with a moistureproof lacquer. The sizing composition hereby illustrated does notimprove the sticking resistance, but, on the other hand, the product is not appreciably poorer in this respect, than the present commercial, untreated product. The economically important gain in width of product is, however, substantial.

The cumar resin is dissolved in the benzene while the sodium oleate is separately dissolved in the water. The resin solution is then added, gradually with violent agitation, to the sodium. oleate solution. A stable emulsion is obtained which contains approximately 25% of resin. This emulsion may be added to the softener bath in amounts suflicient to yield a final resin concentration of about 0.1-0.5%. The amount of softener may be adjusted to approximately d.0-7.0%, depending on the pelliclebeing treated.

Alternatively, the benzene may be removed from the emulsion by evaporation and the resulting aqueous dispersion may be used as the concentrate in preparing the treating bath. This is particularly advantageous where rubber squeeze rolls are used to remove the excess bath. The

treated pellicle is dried as previously described and resembles the product of Example I in its various characteristics. The treated'pellicle of this example is then coated with a moisture-proofing coating composition such as disclosed in the U. S. patent to Charch and Prindle No. 1,737,187.

It is within the scope of this invention, therefore, to provide means for controlling the ultimate width of cellulosic pellicles as they are manufactured, as well as to impart improved surface characteristics. This is of great economic importance in view of the following considerations. Cellulosic pellicles of the type described are frequently destined for use as wrapping tissues. Although they are usually sold by weight, it is important that a given weight of pellicle shall offer as'large an area as possible so that a maximum of covering area will be obtained. As the pellicles are cast, a certain weight of cellulosic material is made available and this weight remains the same whether the pellicle is finally obtained as very wide or relatively narrow. It is therefore economically advantageous to obtain as wide a peliicle as possible with a given weight of celluiosic material and therein lies a very important contributionof the present invention.

It is possible, therefore, in accordance with the present invention, to use considerably narrower apparatus for the forming and purification of the pellicles than is necessary in cases wherein there is considerable shrinkage of the film. More practically, however, it is possible to produce wider pellicles on the existing apparatus thus taking advantage of the facilities for width in such appa ratus. Furthermore it has been found that considerably thinner pellicles can be produced than has been possible heretofore because the shrinkage usually suifered inwidth exerts its effect in the thickness of the pellicle.

It is to be understood that all variations or modifications which conform to the spirit of the invention are intended to be included within the scope of the claims.

I claim: 1

1. In the production of non-fibrous, cellulosic of said pellicles due to the removal of moisture therefrom which comprises treating said pellicles with a liquid containing a shrinkage preventing agent, and drying the said pellicles by contact with the heated surface of a drying element, said agent causing an adhesion between said heated surface and said pellicles during the drying of the latter.

2. In the production of non-fibrous, cellulosic pellicles, the method of restraining the shrinkage of said pellicles due to the removal of moisture therefrom which comprises treating said pellicles while in their undried, gel state with a liquid containing a shrinkage preventing agent, and drying said pellicles by contact with the heated surface of a drying element, said agent causing an adhesion between said heated surface and said pellicles during the drying of the latter.

3. In the production of non-fibrous, cellulosic pellicles, the method of restraining the shrinkage of said pellicles due to the removal of moisture therefrom which comprises treating said pellicles while in their undried, gel state with a liquid containing a shrinkage preventing agent'taken from the group consisting of dewaxed shellac, cumar resins, rosin, salt of rosin acids, alkyd resins, phenol-aldehyde resins and polymerized terpene resins, and drying said pellicles by contact with the heated surface of a drying element, said agent causing an adhesion between said heated surface and said pellicles during the drying of the latter.

4. In the production of non-fibrous, cellulosic pellicles, the method of restraining the shrinkage of said pellicles due to the removal of moisture therefrom which comprises treating said pellicles while in their undried, gel state with a liquid containing an aqueous dispersion of a resin, and drying said pellicles by contact with the heated surface of a drying element, said resin causing an adhesion between said heated surface and said pellicles duringthe drying of the latter.

5'. In the production of non-fibrous, cellulosic pellicles, the method of restraining the shrinkage of said pellicles due to the removal of moisture pellicles, the method of restraining the shrinkage therefrom which comprises treating said pellicles while in their undried, gel state with a liquid containing an aqueous dispersion of a substantially water-insoluble resin, and drying said pellicles by contact with the heated surface of a drying element, said resin causing an adhesion between said heated surface and said pellicles during the dryagent. and drying the said pellicles by contact with the heated surface of a drying element, said agent causing an adhesion between said heated surface and said pellicles during the drying of the latter.

7. In the production of regenerated cellulose pellicles. the method of restraining the shrinkage of said pellicles due to the removal of moisture therefrom which comprises treating said pellicles while in their undried, gel state with a liquid containing a shrinkage preventing agent, and drying said pellicles by contact with the heated surface of a drying element. said agent causing an adhesion between said heated surface and said pellicles during the drying of the latter.

8. In the production of regenerated cellulose pellicles, the method of restraining the shrinkage of said pellicles due to the removal of moisture therefrom which comprises treating said pellicles while in their undried, gel state with a liquid containing a shrinkage preventing agent taken from the group consisting of dewaxed shellac, cumar resins, rosin. salt of rosin acids. alkyd resins, phenol-aldehyde resins and polymerized terpene resins, and drying said pellicles by contact with the heated surface of a drying element, said agent causing an adhesion between said heated surface and said pellicles during the drying of the latter.

9. In the production of regenerated cellulose pellicles, the method of restraining the shrinkage of said pellicles due to the removal of moisture therefrom which comprises treating said pellicles while in their undried, gel state with a liquid containing an aqueous dispersion of a resin, and drying said pellicles by contact with the heated sur face of a drying element, said resin causing an adhesion between said heated surface and said pellicles during the drying of the latter.

10. In the production, of regenerated cellulose pellicles, the method of restraining the shrinkage of said pellicles due to the removal of moisture therefrom which comprises treating said pellicles while in their undried, gel state with a liquid containing an aqueous dispersion of a substantially water-insoluble resin, and drying said pellicles by contact with the heated surface of a drying element, said resin causing an adhesion between said heated surface and said pellicles during the drying of the latter.

DONALD E. DREW. 

